One example of an electromagnetic signal source is a wireless access point, such as a Wi-Fi base station (Wireless Access Point), which is used to communicate wirelessly with a device by the transmission and reception of electromagnetic radiation in the form of radio waves. Other electromagnetic signal sources may for example include optical (infra-red) communication devices and electromagnetic/wireless beacons of various sorts, including connectable and non-connectable beacons according to the Bluetooth short range wireless connectivity standard specification (Bluetooth beacons).
It is known to use electromagnetic signal sources, such as WAPs and Bluetooth Beacons, to estimate the position of a device (typically a mobile device). It is known to maintain a master database concerning the position of WAPs and other electromagnetic signal sources across a wide geographical area (e.g. a country, a land mass, the world etc.) and to use this master database to provide a positioning system to determine the position of (typically mobile) devices. Such master databases typically also specify an identifier of each WAP (e.g. MAC address) and typically also a measurement of transmitted signal strength. Thus, for example, a smartphone with Wi-Fi capability can determine the identity and signal strength of adjacent WAPs and Bluetooth beacons, and a triangulation can be carried out based on the known locations of the electromagnetic signal sources in question in order to determine the location of the smartphone (and hence user).
It is also known to update said master databases using data obtained from mobile devices, for example, mobile devices carried by users of the positioning system. The updates may include identifying new WAPs and other electromagnetic signal sources, making measurements helpful to improving estimates of the position of WAPs and other electromagnetic sources, and identifying changes in electromagnetic sources, for example that an electromagnetic signal source has moved or disappeared.
Such procedures can be useful for improving data which has already been obtained in a systematic survey, or detecting errors arising from movement or disappearance of an electromagnetic signal sources. However, they cannot be readily used to extend data into regions where existing master databases have significant gaps (referred to herein as void zones). It is generally required for an initial survey to be carried out before positioning will function successfully in a new zone, particularly an indoor zone, such as a shopping centre, where satellite positioning systems are generally unavailable. This means that users of existing systems may find themselves unable to use a given positioning system despite the presence of temporarily or permanently stationary electromagnetic sources which could be detected by their mobile device.
In some systems, relatively detailed data may be transmitted from a mobile device to the server or servers responsible for providing access to the master databases mentioned above. There is an incentive to provide more detailed data to allow more advanced processing and location estimation to be carried out by the server, especially if readings from multiple users are being combined. Indeed, there is a further incentive to widen user participation to improve the accuracy of estimates, but the pressure to include data from more users and to provide more detailed information results in a vast amount of data being sent to the location server. To make the processing of such data more efficient—and in some cases possible at all—existing systems typically process the received data in batches on a periodic basis, for example every day or every week. In this way, the master database is slowly updated with new information.
US2008/0176583 describes methods and systems for selecting and providing a relevant subset of Wi-Fi location information indicative of estimated positions of Wi-Fi Access Points to a mobile client device so that the client device may estimate its position with efficient utilization of resources. US2008/0176583 also teaches that data received from client devices can be used to update information stored with respect to Wi-Fi Access Points. However, no teaching is provided of how to cope with the vast amount of data which may be gathered from a plurality of user devices in such a situation.
US2011/0026506 describes systems and methods for collecting information at a server pertaining to the configuration of one or more wireless networks. Also disclosed in US2011/0026506 are methods for collecting information responsive to the coverage or quality of the wireless network configuration information already stored in a network database. However, the method of US2011/0026506 involves discarding collected information which is not being actively sought by the server before it is provided to the server which leads to the loss of potentially useful information.
WO2011/077166 provides a teaching of a method of estimating the location of a plurality of electromagnetic signal sources comprising: scanning at a first plurality of locations to generate signal source position data, the signal source position data representing estimates of the position of at least one of said signal sources; scanning at a second plurality of locations using a signal detection system to generate signal detection data, the signal detection data relating to signals received at the second plurality of locations from the signal sources; processing the signal source position data in dependence on the signal detection data to correct estimation errors in the signal source position data; and outputting the processed signal source position data. However, WO2011/077166 involves processing the signal source position data in a batch. This means that there is typically a lengthy delay between the detection of an electromagnetic signal source which was previously unknown and the availability of its position for use in estimation of the position of a user device.
GB2323988 describes a method of refining the estimate of the position of a satellite for use in a satellite positioning system. However, data from a plurality of user devices is processed in a batch before the refined estimate of the position of a satellite can be used in the estimation of a position of a mobile device, leading to a significant delay before the refined estimate of the position of the satellite can be used in estimating the position of a mobile device. In addition, a further positioning system is needed to provide an initial estimate of the position of the satellite.
The present invention seeks to address these and other problems in the prior art.